The present invention relates to a control system for an internal combustion engine having a plurality of cylinders and a cylinder halting mechanism for halting the operation of some of the plurality of cylinders.
In an internal combustion engine having a cylinder halting mechanism for halting the operation of some of a plurality of cylinders, if fuel is erroneously supplied to a nonoperating cylinder, the amount of fuel supplied into another operating cylinder increases. This makes the air-fuel ratio deviate from a desired value and causes deterioration of the exhaust gas characteristics.
The above-described situation occurs when the cylinders do not actually operate although a control signal for operating all cylinders is supplied from the control system to the cylinder halting mechanism. Therefore, this failure must be detected rapidly. For example, the following method for determining such a failure is disclosed in Japanese Patent Laid-open No. Hei 6-146937. In the method, a discrimination threshold value PMAP corresponding to an intake pressure of the engine, which is operated in the all-cylinder operating mode, is calculated according to the engine speed and the throttle valve opening. If a control signal for operating all cylinders is outputted to the cylinder halting mechanism and the detected intake pressure PB is higher than the discrimination threshold value PMAP, it is determined that some of the cylinders are not actually operating, or in other words, the cylinder halting mechanism is in failure.
However, the intake pressure PB is always changing in response to operation of the intake valve of each cylinder and the difference between the average value of intake pressures detected during all-cylinder operation of the engine and the average value of intake pressures detected during partial-cylinder operation where some of the cylinders are not operating, is small. Therefore, there is a high possibility of erroneously determining that the cylinder halting mechanism is in failure although the mechanism is operating normally.
It is an object of the present invention to provide a control system for an internal combustion engine which can determine the failure of the cylinder halting mechanism more accurately.
In order to attain the object described above, the present invention provides a control system for an internal combustion engine having a plurality of cylinders and a cylinder halting mechanism for halting operation of some or at least one of the plurality of cylinders. The control system comprises operation instructing means, intake pressure detecting means, and operating state detecting means. The operation instructing means instructs the cylinder halting mechanism to operate all of the plurality of cylinders or to halt the operation of at least one of the plurality of cylinders. The intake pressure detecting means for detects the intake pressure of the engine. The operating state detecting means detects the operating state of the cylinder halting mechanism based on the amount of change (PB3) in the output of the intake pressure detecting means.
With this configuration, the intake pressure of the engine is detected and the operating state of the cylinder halting mechanism is detected based on the amount change in the detected intake pressure. Therefore, a failure of the cylinder halting mechanism can be determined with a higher accuracy when compared with detecting the operating state of the cylinder halting mechanism based on the intake pressure itself.
Preferably, the control system further comprises fuel supply stopping means for stopping the fuel supply to some of the plurality of cylinders, if it is detected by the operating state detecting means that some of the plurality of cylinders are not operating although the operation instructing means instructs the cylinder halting mechanism to operate all of the plurality of cylinders.
With this configuration, the fuel supply to some of the plurality of cylinders is stopped, if it is detected by the operating state detecting means that some of the plurality of cylinders are not operating although the operation instructing means instructs the cylinder halting mechanism to operate all of the plurality of cylinders. Consequently, a situation where the amount of fuel to be supplied to each of the operating cylinders is increased and the air-fuel ratio deviates from its desired value to deteriorate the exhaust gas characteristics, can be avoided.
Preferably, the operating state detecting means determines that some of the plurality of cylinders are not operating when an absolute value (|PB3|) of the amount of change in the detected intake pressure is greater than a predetermined value (PBTH).
Preferably, the intake pressure detecting means detects the intake pressure at a time at which the piston of any cylinder of the plurality of cylinders is positioned in the proximity of the top dead center thereof.
Preferably, the operating state detecting means stores a predetermined number of the amounts of change in the detected intake pressure and detects the operating state of the cylinder halting mechanism based on an average value of the stored amounts of change in the detected intake pressure, the predetermined number being set according to the number of the cylinders (one half of the number of the cylinders).